The present invention relates to a process for the preparation of N-halogenated phenyl maleimides, particularly N-brominated or N-chlorinated phenylmaleimide by reacting molten maleic anhydride with a brominated or chlorinated aniline at certain molar ratios in the presence of a tin (Sn) containing catalyst and optionally in the presence of an inert solvent.
A relatively few number of prior art processes have been proposed for the preparation of N-halogenated phenylmaleimide compounds and especially the N-brominated and N-chlorinated phenylmaleimides by catalytically reacting maleic anhydride with a halogenated aniline.
British Pat. No. 1,533,068 describes a process of preparing N-arylmaleimides including N-(chlorophenyl) maleimide by reacting maleic anyhydride with an arylamine and then dehydrating the resulting N-arylmaleic acid amide for a cyclization in the presence of an acid catalyst in an inert solvent without separating the N-arylmaleic acid amide from the reaction mixture, the dehydration being carried out under conditions of azeotropic distillation.
Czechoslovakian Pat. No. 171,593 describes the preparation of halogenated derivations of N-phenylmaleimide at temperatures of 210.degree. C. in the presence or absence of a zinc chloride catalyst.
U.S. Pat. No. 4,508,883 also describes the preparation of N-(2,4,6-tribromophenyl)maleimide by reacting 2,4,6-tribromoaniline and maleic anhydride in the presence of a zinc chloride catalyst.
The N-brominated or chlorinated phenyl maleimides prepared by the process of this invention are useful as fire retardant additives or for the formation of copolymers with, for example, bromostyrene as described in U.S. Pat. No. 4,508,883.